散装熟肉制品中单增李斯特菌污染状况分析

目的分析散装熟肉制品中单增李斯特菌污染状况。方法根据GB 4789.30-2016《单核细胞增生李斯特氏菌检验》规定的方法对散装熟肉制品的加工用原料、生产环境、各加工环节中产品以及不同销售环境下产品中的单增李斯特菌进行定性和定量检测。结果原料肉的总体带菌率达到21%;生产环境中第三区(远离食品接触面的区域)检出率为2%,其余区域未检出;各加工环节中产品单增李斯特菌检测结果均小于10CFU/g;不同销售环境下产品中单增李斯特菌检测结果小于10 CFU/g的比例为93%,处于10～50 CFU/g之间的样本占比6%,大于50 CFU/g的占比为1%。结论原料散装熟肉制品中单增李斯特菌污染的主要来源,蒸煮等加工环节能有效地杀灭单增李斯特菌。销售环境也关系到散装熟肉制品单增李斯特菌的污染程度,对于未包装的产品,专卖店优于农产品市场。     

Growth kinetics of Listeria monocytogenes in broth and beef frankfurters--determination of lag phase duration and exponential growth rate under isothermal conditions

ABSTRACT:  The objective of this study was to develop a new kinetic model to describe the isothermal growth of microorganisms. The new model was tested with Listeria monocytogenes in tryptic soy broth and frankfurters, and compared with 2 commonly used models—Baranyi and modified Gompertz models. Bias factor (BF), accuracy factor (AF), and root mean square errors (RMSE) were used to evaluate the 3 models. Either in broth or in frankfurter samples, there were no significant differences in BF (approximately 1.0) and AF (1.02 to 1.04) among the 3 models. In broth, the mean RMSE of the new model was very close to that of the Baranyi model, but significantly lower than that of the modified Gompertz model. However, in frankfurters, there were no significant differences in the mean RMSE values among the 3 models. These results suggest that these models are equally capable of describing isothermal bacterial growth curves. Almost identical to the Baranyi model in the exponential and stationary phases, the new model has a more identifiable lag phase and also suggests that the bacteria population would increase exponentially until the population approaches to within 1 to 2 logs from the stationary phase. In general, there is no significant difference in the means of the lag phase duration and specific growth rate between the new and Baranyi models, but both are significantly lower than those determined from the modified Gompertz models. The model developed in this study is directly derived from the isothermal growth characteristics and is more accurate in describing the kinetics of bacterial growth in foods.     

鲜切结球莴苣中单增李斯特菌生长预测模型的建立

为建立不同温度下鲜切结球莴苣中单增李斯特菌生长模型,将单增李斯特菌接种到鲜切结球莴苣表面,并于不同温度下贮藏,获得其在4、8、16、24和32℃下的生长数据,选用Gompertz模型进行拟合,建立初级生长模型。在此基础上建立二级模型研究温度对初级模型中单增李斯特菌生长动力学参数的影响,并进行数学检验。结果表明,对最大比生长速率和延滞时间建立平方根模型,结果呈良好的线性关系,相关系数R2分别为0.977 2和0.984 7,所建立的预测模型能很好地描述不同温度下单增李斯特菌的生长动态。     

单核细胞增生李斯特菌在典型食品接触表面的存活建模研究

单核细胞增生李斯特菌在食品接触表面的长期存活,可导致其在食品中暴露可能性升高,增加引发严重食源性疾病的风险。本文研究了无营养冷藏（4 ℃）和室温（25 ℃）条件下,单核细胞增生李斯特菌在7种典型食品接触材质表面的存活情况。同时采用失活模型Bigelow模型进行拟合,便于理解其存活动力学。结果发现,单核细胞增生李斯特菌在木材质表面上的存活时间较短,但在其他材质表面可存活46 h以上。显著性分析表明,除玻璃和ABS塑料材质外,单核细胞增生李斯特菌在4 ℃条件下较25 ℃条件下存活量更高,表明冷藏环境有助于其长期存活。同时,单核细胞增生李斯特菌在玻璃和聚丙烯表面的存活能力相对较强。因此,为了更准确地推断单核细胞增生李斯特菌在食品链中导致危害发生的可能性,应纳入对其在不同材质及不同温度组合环境下存活能力的考量。     

Modelling thermal inactivation of Listeria monocytogenes in sucrose solutions of various water activities

The heat resistance of Listeria monocytogenes was determined in sucrose solutions with water activity (a(w)) ranging from 0.99 to 0.90. At all temperatures investigated shape of the survival curves depended on the a(w) of the treatment medium. The survival curves for a(w)=0.99 appeared to be linear, for a(w)=0.96 were slightly upwardly concaved and for a(w)=0.93 and 0.90 were markedly concave upward. A mathematical model based on the Weibull distribution provided a good fit for all the survival curves obtained in this investigation. The effect of the temperature and a(w) on the Weibull model parameters was also studied. The shape parameter (p) depended on the a(w) of the treatment medium but in each medium of different a(w) the temperature did not have a significant effect on this parameter. The p parameter followed a linear relationship with a(w). The scale parameter (delta) decreased with the temperature following an exponential relationship and increased by decreasing the a(w) in the range from 0.99 to 0.93. However the delta parameter of survival curves obtained at a(w)=0.90 were lower than those obtained at a(w)=0.93. A mathematical model based on the Weibull parameters was built to describe the joint effect of temperature and a(w) on thermal inactivation of L. monocytogenes. This model provides a more complete information on the influence of the a(w) on the L. monocytogenes than the data initially generated. The model developed indicated that the effect of the a(w) on the thermal resistance of L. monocytogenes varied depending upon the temperature of treatment.     

预包装熟肉制品生产加工过程单核细胞增生李斯特菌污染及病原学特征分析

目的 了解预包装熟肉制品生产加工过程各个环节中单核细胞增生李斯特菌(以下简称单增李斯特菌)污染水平,并分析分离菌株的分子特征及药敏特征,对企业生产质量控制环节提出预防控制措施.方法 2015-2017年在德州市某预包装熟肉制品厂采集生产加工过程中熟肉制品原辅料、中间产品、成品、终产品和环境样品共计460份,依据GB 4...     

2010~2016年云南省熟肉制品和餐饮食品中单增李斯特菌污染情况调查分析

目的 了解2010～2016年云南省市售熟肉制品和餐饮食品中单增李斯特菌污染情况调查分析。方法 在全省16个州市县中选取超市、农贸市场、零售及餐饮环节等为采样点, 随机采取熟肉制品1465份和餐饮食品3674份, 按照GB 4789.30-2010《食品安全国家标准 食品微生物学检验 单核细胞增生李斯特氏菌检验》及《全国食源性致病菌监测工作手册》进行检测和鉴定。结果 1465份熟肉制品中单增李斯特菌检出率为2.18%(32/1465), 3674份餐饮食品中单增李斯特菌阳性率为1.44%(53/3674)。在不同流通环节中, 熟肉制品和餐饮制品中检出率最高的分别为便利店和超市, 分别为9.09%(5/55)和1.67%(3/180)。在不同的监测地区, 熟肉制品和餐饮制品检出率最高均为昭通地区, 分别为7.8%(11/141)和7.17%(18/251)。结论 单增李斯特菌在熟肉制品及餐饮食品中均有检出, 说明云南省的食品中存在一定的单增李斯特菌污染, 对消费者的安全有潜在风险, 相关监管部门应持续加强监管, 预防食源性疾病的发生。     

市售小酥肉中沙门菌热失活模型的建立与验证

目的 研究不同加热温度下小酥肉中沙门菌的热失活规律,以期为安全消费提供指导。方法 将接种10⁸ CFU/g鼠伤寒沙门菌的小酥肉在80℃、90℃、100℃、110℃和120℃,热处理一定时间后活菌计数,使用线性模型、Logistic模型和Weibull模型对小酥肉中沙门菌的热失活规律进行研究,并通过外部实验对模型进行验证。结果 与线性模型和Logistic模型相比,Weibull模型更适用于描述小酥肉中沙门菌热失活状况,其一级模型判定系数R²均在0.992 1以上,二级模型R²分别为0.949 2、0.995 9,用95℃和105℃温度对模型进行验证时的准确度Af、偏差度Bf均在可接受范围内,说明实验构建的模型可较好地描述80℃～120℃温度范围内小酥肉中沙门菌的失活规律。结论 本研究有望为小酥肉安全加热时间提供参考,同时为小酥肉微生物相关风险评估提供模型支持。     

微生物预测模型研究及其在肉品工业中的应用

预测微生物的数学模型可以对食品中微生物的生长、残存和死亡进行数量化预测.简述了预测微生物的数学模型研究食品微生物行为的理由.介绍了微生物预测模型的研究概况及其在肉类工业中的应用情况.对目前存在的问题和未来的发展进行了分析和总结.     

盐水鸭中单核细胞增生李斯特菌生长预测模型的建立

为研究盐水鸭中单核细胞增生李斯特菌(Listeriamonocytogenes,Lm)的生长规律,通过测定4、10、16、25℃条件下的生长数据,选用4种常用的一级模型(Gompertz、Logistic、Richards及MMF模型)对数据进行拟合,比较各模型决定系数R^2和均方误差(MSE),确定最适一级模型,根据一级模型得到的最大比生长速率(μmax)和迟滞期(λ)建立与温度相关的二级模型。结果表明:Gompertz模型拟合的生长曲线R^2均达到0.99以上,为最适一级模型,在25℃条件下,Lm经0.78 h后即进入对数期,从4℃提高到10℃时,生长速率从0.02 1g(cfu/g)·h^-1增至0.05 1g(cfu/g)·h^-1,说明温度对盐水鸭中Lm的生长影响较大。选用Ratkowsky平方根模型建立的温度与μmax关系的二级模型R^2为0.98,偏差因子(Bf)、准确因子(Af)分别为0.99、1.01,二次多项式模型建立的温度与λ关系的R^2为0.99,Bf、Af分别为1.01、1.08,表明所建两种模型均能较好地描述盐水鸭中Lm的生长情况。本研究建立的生长模型可为监控盐水鸭的食品安全和风险评估提供参考。     

Modelling growth of Lactobacillus plantarum and shelf life of vacuum‐packaged cooked chopped pork at different temperatures

Lactobacillus plantarum growth in a vacuum‐packaged cooked meat product under different storage temperatures (4, 10 and 16 °C) and the relation between the microorganism growth and sensory quality were investigated. The Gompertz model was fitted to experimental counts of L. plantarum showing a good fitting to growth curves at different temperatures. A root‐square secondary model and linear model were satisfactorily fitted to estimated growth rates () and lag times (), respectively. The sensory attributes (colour, flavour, taste, appearance) were also evaluated due to their importance to the global quality (Q). The sensory deterioration was detected several days after L. plantarum reached the stationary phase, that is, 59, 45 and 25 days for 4, 10 and 16 °C, respectively. According to results, sensory deterioration was related to time when microorganism reached late stationary phase, phenomenon known as ‘delayed change’.     

Comparing predicting models for heat inactivation of Listeria monocytogenes and Pseudomonas aeruginosa at different pH

Under the same experimental conditions it has been demonstrated that whereas survival curves of Listeria monocytogenes in the range of temperatures from 54 to 62 °C followed a first-order kinetic, those of Pseudomonas aeruginosa in the range of temperatures from 50 to 56 °C were not linear showing a shoulder followed by a linear region. The first order kinetic model did not describe survival curves of P. aeruginosa. A model based on the Weibull distribution (Log₁₀(N_t/N₀)=(1/−2.303)*(t/b)ⁿ)) accurately described the inactivation kinetics of both microorganisms at the three pHs of 4, 5.5, 7.4 investigated. For both microorganisms, the b value depended on the treatment temperature and the pH of the treatment medium. Whereas for L. monocytogenes the n value was independent of the treatment conditions, for P. aeruginosa the n value depended on the pH of the treatment medium.

The model based on the Weibull distribution was capable of accurately predicting the treatment time to inactivate five Log₁₀ cycles of both microorganisms at the three pHs investigated.     

Effect of Filling Type and Heating Method on Prevalence of Listeria species and Listeria monocytogenes in Dumplings Produced in Poland

The count of Listeria monocytogenes was determined, before and after heat treatment, in 200 samples of dumplings of 9 brands and with different types of stuffing. Analyses were conducted according to ISO 11290–1 standard and with real‐time PCR method. The highest count of L. monocytogenes was found in meat dumplings (10² to 10⁴ CFU/g), whereas products with white cheese‐potato stuffing and vegetable‐mushroom stuffing contained significantly less Listeria, 20 to 80 and 5 to 32 CFU/g, respectively. In cooled meat dumplings the extent of contamination depended significantly on the producer. In addition, a significant (P < 0.05) correlation was determined between contamination level and meat content in the stuffing (rho = 0.418), especially in stuffing containing pork meat (0.464), contrary to beef‐containing stuffing (0.284). Heating dumplings in boiling water for 2 min completely eliminated L. monocytogenes in meat dumplings. In contrast, the microwave heating applied for 2 min at 600 W only reduced the count of L. monocytogenes by 1 to 2 logs. Hence, the microwave heating failed to reduce the risk of infection with this pathogen below the level permissible in the EU regulation, especially in the most contaminated samples. In this case, the efficacy of microwave heating was significantly (P < 0.05) affected by the initial count of L. monocytogenes (rho = 0.626), then by meat content in the stuffing (0.476), and to the lowest extent—by the type of meat (0.415 to 0.425). However, no Listeria sp. and L. monocytogenes were isolated from cooked dumplings with fruits (strawberries or blueberries).     

Predictive model for growth of Clostridium perfringens during cooling of cooked uncured beef

This paper considers growth models including one based on Baranyi's equations for growth and the other based on the logistic function. Using a common approach for constructing dynamic models for predicting Clostridium perfringens growth in ready-to-eat uncured beef during cooling, there was no appreciable difference between the models' predictions when the population of cells was within the lag or exponential phases of growth. The developed models can be used for designing safe cooling processes; however, the discrepancies between predicted and observed growths obtained in this study, together with discrepancies reported in other papers using the same, or similar methodology as used in this paper, point to a possible inadequacy of the derived models. In particular, the appropriateness of the methodology depends on the appropriateness of using estimated growth kinetics obtained from experiments conducted in isothermal environments for determining coefficients of differential equations that are used for predicting growth in constantly changing (dynamic) environments. The coefficients are interpreted as instantaneous specific rates of change that are independent of prior history. However, there is no known scientific reason that would imply the truth of this assumption. Incorporating a different, less restrictive assumption, allowing for a dependency on the prior history of cells for these kinetic parameters, might lead to models that provide more accurate estimates of growth. For example, a cooling scenario of 54.4-27 degrees C in 1.5h, the average predicted and observed log(10) relative growths were 1.1log(10) and 0.66log(10), respectively, a difference of 0.44log(10,) whereas, when assuming a particular dependency of history, the predicted value was 0.8log(10). More research is needed to characterize the behavior of growth kinetic parameters relative to prior history in dynamic environments.     

Inactivation Kinetics of Listeria monocytogenes by High-Pressure Processing: Pressure and Temperature Variation

The enhanced quasi-chemical kinetics (EQCK) model is presented as a methodology to evaluate the nonlinear inactivation kinetics of baro-resistant Listeria monocytogenes in a surrogate protein food system by high-pressure processing (HPP) for various combinations of pressure (P= 207 to 414 MPa) and temperature (T= 20 to 50 °C). The EQCK model is based on ordinary differential equations derived from 6 "quasi-chemical reaction" steps. The EQCK model continuously fits the conventional stages of the microbial lifecycle: lag, growth, stationary phase, and death; and tailing. Depending on the conditions, the inactivation kinetics of L. monocytogenes by HPP show a lag, inactivation, and tailing. Accordingly, we developed a customized, 4-step subset version of the EQCK model sufficient to evaluate the HPP inactivation kinetics of L. monocytogenes and obtain values for the model parameters of lag (λ), inactivation rate (μ), rate constants (k), and "processing time" (tp). This latter parameter was developed uniquely to evaluate kinetics data showing tailing. Secondary models are developed by interrelating the fitting parameters with experimental parameters, and Monte Carlo simulations are used to evaluate parameter reproducibility. This 4-step model is also compared with the empirical Weibull and Polylog models. The success of the EQCK model (as its 4-step subset) for the HPP inactivation kinetics of baro-resistant L. monocytogenes showing tailing establishes several advantages of the EQCK modeling approach for investigating nonlinear microbial inactivation kinetics, and it has implications for determining mechanisms of bacterial spore inactivation by HPP. Practical Application: Results of this study will be useful to the many segments of the food processing industry (ready-to-eat meats, fresh produce, seafood, dairy) concerned with ensuring the safety of consumers from the health hazards of Listeria monocytogenes, particularly through the use of emerging food preservation technologies such as high-pressure processing.     

Microwave heating of cooked pork patties as a function of fat content

ABSTRACT:  In this study, the parameters heating rate, dielectric factors, and specific heat capacity, which determine the heating profiles and the dissipation of energy during microwave heating, were obtained for precooked pork patties. The pork patties studied were lean meat, pure back fat, and several lean meat/back fat mixtures. Microwave heating at 798 W power was not sufficient to accelerate the heating rates in 100% lean meat compared to 415 W. However, samples were able to heat up faster and dissipate more energy at 798 W power as fat content increased and moisture content decreased. The recorded differences in the specific heat capacity of the studied materials as a function of temperature seemed not to be the key factor to explain the observed temperature rises. Temperature rise seemed to have more to do with the interactions of fat with the electromagnetic field, and with viscosity changes during phase transitions. Trends found for the dielectric properties over microwave heating of meat products agree with data from other authors, but the influence of parameters related to the sample composition and structure should be taken into account. The dissipation factors (ɛ"/ɛ') provided a good approximation to the capacity of the samples containing lean meat and the lean meat/fat mixtures to transform the electromagnetic energy into heat. Neither the dielectric constant nor the loss or dissipation factors were able to clarify the high amount of energy transformed into heat in 100% back fat. Penetration depth and reflected power indicated that back fat allowed microwave energy to be repeatedly redirected to the material.     

Factors influencing resuscitation and growth of heat injured Listeria monocytogenes 13-249 in sous vide cooked beef

The growth of Listeria monocytogenes 13-249 in vacuum-packed, minced beef was investigated as a function of degree of heat injury (including no injury i.e. uncooked beef), growth phase (logarithmic and late stationary phase), pH (5.6 and 6.2), and storage temperature (3, 10 and 20 degrees C) during a storage period of 30 days. Late logarithmic and late stationary phase cultures of L. monocytogenes 13-249 showed similar growth in refrigerated, vacuum-packed, raw minced beef with a high pH (6.2). In normal pH (5.6) beef there was no growth at 3 degrees C while growth at 10 and 20 degrees C was only observed for logarithmic phase cultures. Heat injured late stationary phase cultures with 95-99.9% injured cells in the surviving population (as measured by differential plating on enriched vs. selective media after sous vide cooking) did not grow or repair sublethal injuries in sous vide cooked beef at 3 degrees C while repair and growth took place at 10 as well as at 20 degrees C. In logarithmic phase cultures heat injury occurred very rapidly and > or = 99.9% heat injury was observed in all trials in spite of much lower pasteurization values and fewer log10 reductions compared with late stationary phase cultures. Regardless of growth phase, all cultures where a high degree of heat injury (> or = 99.9%) was observed, did not subsequently grow in the beef product at 3 or 10 degrees C within 30 days. Growth of heat injured cultures preexposed to heat shock (46 degrees C, 30 min) or slowly rising temperatures (0.3 degrees C min(-1)) before heat injury was also investigated. Heat shocked or heat adapted cultures generally responded in the same manner as non-stressed cultures (no growth at 3 degrees C) except that a longer lag phase was observed in beef processed at slowly rising temperatures and in normal pH beef at 10 degrees C. Although processing at slowly rising temperatures may slightly increase the survival of L. monocytogenes 13-249 in cooked beef, there seem to be no indication of an increase in subsequent growth potential of the surviving cells.